The RTM process is a molding method including: laying a workpiece made of composite material, such as reinforcing fiber base material (glass fiber, carbon fiber, or the like), on a mold; hermetically sealing a vacuum bag film or mold with the preform member placed therein; and injecting resin into the resultant vacuum bag film or mold through vacuum suction to impregnate the preform member with the resin. The use of the RTM process has an advantage which makes it possible to mold the composite material at low cost without a need of an expensive autoclave or the like.
There are cases where pre-heating is performed as a step of the RTM process. The pre-heating is to heat a preform member, making it easy for the preform member to be impregnated with resin.